The present invention relates to a circulating fluidized bed reactor in which solid particles are separated from the flue gas and recycled to the reactor chamber. The invention may also be used in gasifiers.
In known circulating fluidized bed reactors, flue gas is removed from the upper end of the reactor chamber through a duct to a cyclone separator. Entrained ash, unburned solid fuel, and other relatively coarse particles, are separated from the hot flue gas and are returned to the lower part of the reactor chamber. Before the flue gas is discharged through a stack, it is passed through a dust collector of suitable design for removal of fine particles. Previously, the separation and collection of dust particles have been achieved by various apparatus which have required substantial space and multiple flow lines interconnecting their various elements. Integrating these various elements and functions into a substantially compact system has not heretofore been achieved.
In accordance with the present invention, there is provided a reactor having integrated therewith in a single vessel vertical filtration tubes for separating solids from the solids-entrained gases. These tubes are made of porous super alloys or ceramics, and which tubes are disposed in a filter housing located in back-to-back relation with the reactor chamber. The filtration tubes are used to clean the flue gas.
In certain applications, a pre-separator is located above the filter housing in direct communication with the flue gas discharge outlet. The pre-separator is thus located in back-to-back relation with the upper end of the reactor chamber. The pre-separator is used to separate relatively coarse particles from the flue gas and return them to the reactor chamber before the gas enters the filtration tubes. The smaller sized solid particles separate from the solids-entrained gas as the gas passes through the porous tubes. Such solids remain within the tubes along the inner walls thereof and are transported by the residual gas flow through the tubes for return to the reactor chamber. The structure and function of the filter apparatus which affords a thorough cleaning of the gas as it passes through the porous walls of the tubes are described in U.S. Pat. No. 4,584,003, the disclosure of which is incorporated herein by reference.
Further, in accordance with the present invention, two different types of pre-separators may be used in keeping with the compact nature of the reactor hereof. In a first type, the filtration tubes project above an inclined wall into an area in communication with the flue gas discharge outlet. The upper ends of the tubes are partially closed. In this manner, the change of direction of the flue gas causes separation of the coarse particles which are deposited on an inclined wall forming the top of the filter housing for conveyance back to the reactor chamber. The gas with the smaller size solids flows into the filtration tubes and through a plurality of compartments formed in the housing. Each compartment is connected with a clean gas outlet for flow out of the vessel.
In another form hereof, the pre-separator may comprise a cyclone separator disposed on top of the filter housing. An inlet duct is in communication with the gas discharge outlet for tangentially introducing gas into the cyclone separator. An inner tube of the separator extends upwardly into the cyclone and opens through an inclined wall into a chamber in communication with the filtration tubes. The solids fall onto the inclined wall for return to the reactor chamber, whereas the gas flows into the upwardly projecting tube for flow through and separation from the solids entrained therein by the filtration tubes.
From the foregoing, it will be appreciated that the reactor chamber and the filter housing, together with the pre-separator on top of the filter housing in certain applications, lie in back-to-back relation one to the other, thereby affording a compact unitary vessel. In this manner, the combined and integrated reactor and filter housing may be enclosed within a pressurized vessel.
In another form of the present invention, a pair of filter housings may lie on opposite sides of the reactor chamber. Thus, each filter housing lies in back-to-back relation with the centralized reactor chamber. Each may have a pre-separator of either of the foregoing described type, depending upon the application. Each filter housing has outlet conduits for transporting the clean gas from the space between the filtration tubes and the housing externally to the vessel. The solids which are separated in any pre-separator fall by gravity along the inclined wall into the central reactor chamber while the solids separated from the solids-entrained gas in the filtration tubes flows toward the base of the reactor chamber for return thereto.
In a further form of the present invention, whether the reactor chamber and filter housing lie in back to back relation or the filter housing straddles the reactor chamber, the coarse solids may be recirculated through discrete pipes which form part of the filter assembly. The coarse solids exiting the discrete filter assembly pipes may be recombined with the finer dust particles flowing through the other filter pipes for combined flow into the combustion chamber. Alternatively, the coarse and fine solids may be introduced into the combustion chamber separately.
In a preferred embodiment of the present invention, the reactor chamber and filter housing are enclosed in a pressure-proof vessel, preferably cylindrical. Also, the reactor is supplied with compressed air and the cleaned flue gas is used in a gas turbine. It will be further appreciated that the principles of the present invention can likewise be applied to a gasifier rather than a fluidized bed reactor.
In certain fluidized bed reactor applications, solid particles may adhere to the inner surface of the filtration tubes, tending to clog the tubes and inhibit the flow of gas through the tubes. While a pressure pulse may be provided in the gas outlet pipes to momentarily change the direction of the gas flow through the porous tubes and thereby loosen the particles adhering to the inner surfaces of the tubes, it has been recognized that such solid particles afford a beneficial scrubbing effect on the tubes. Consequently, in certain applications, the scrubbing effect of the solid particles as they move through the tubes tend to clean the tubes and keep the pores free of clogging material. Thus, in certain applications, a pre-separator may not be used and the larger particles, separated in other applications by the pre-separator, are particularly directed for flow through the filtration tubes to scour the inside of the tubes and maintain such surfaces clean. More particularly, this is achieved by providing enlarged inlet openings to the porous tubes such that additional quantities, particularly of the larger materials, may flow through the tubes to clean the latter and for ultimate return to the fluidized bed combustion chamber.
In a still further form of the present invention, the filter housing is comprised of a plurality of porous plates. The plates may have ribs projecting from one side thereof. When the plates are aligned generally vertical one with the other, the free edges of the ribs engage the back side of the adjacent plate to form a plurality of passageways. Certain of the passageways communicate with the filter housing gas inlet at the top of the filter such that gas may flow through the passageways and through the porous plates into other passageways formed by the juxtaposition of the plates. These latter passageways are closed at both the top and bottom of the filter housing and have communicating conduits for collecting the filtered clean gas flowing into such passageways for flow to a clean gas outlet. Alternatively, the filter housing may be formed of solid porous material having a plurality of bores formed therein whereby gas flows into those bores in communication with the gas inlet at the top of the housing and through the porous filter housing into those bores closed at the top and bottom of the housing for flow of clean gas to the clean gas outlet.
In accordance with a specific preferred embodiment of the present invention, there is provided a circulating fluidized bed reactor comprising means defining an upright reactor chamber having at least one gas discharge opening adjacent its upper end and at least one inlet opening for solids separated from the gas adjacent its lower end. There is also provided a filter housing and means defining a plurality of generally vertically extending horizontally spaced passageways, these passageway defining means in part formed of porous material and disposed in the housing. The housing and the reactor chamber are arranged in back-to-back relation one with the other. The housing has a gas inlet in communication with the gas discharge opening and the passageways, a solids outlet in communication with the solids inlet opening, at least one clean gas outlet, and means in the housing in communication with the one clean gas outlet for communicating gas flowing through the porous material of the passageways with the one clean gas outlet.
In a preferred form of the invention for certain applications, the gas inlet includes means defining larger inlet openings for the passageways than the internal diameter of the passageways to provide a solids scrubbing action along the inside surfaces of the passageways to minimize clogging. Preferably, the inlet opening means are generally funnel-shaped elements, thereby increasing the quantity of solids flowing through the passageways in comparison with the quantity of solids which would flow through the passageways if the inlet openings were of the same diameter as the passageways. That is to say, the inlets for each of the passageways have combined cross-sectional areas greater than the combined cross-sectional areas of the passageways to provide enhanced scrubbing of the solids along the interior surfaces of the passageways.
In a further aspect of the present invention, there is provided a method for separating solids entrained in a gas from a fluidized bed reactor comprising the steps of forming a filter comprised of a plurality of spaced passageways of porous material, disposing the filter in a housing, disposing the housing in back-to-back relation with the reaction chamber, flowing the gas with entrained solids through a gas discharge opening in the reactor and into the passageways for flow of the gas through the porous material to clean the gas, collecting the clean gas flowed through the porous material and returning solids separated from the gas within the passageways to the reactor chamber.
Accordingly, it is a primary object of the present invention to provide a novel and improved compact circulating fluidized bed reactor design with separator, particularly a circulating fluidized bed reactor design with separator suited for use in pressurized combustion or other processes, as well as a method of operating the reactor.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.